The Memory Event Horizon is the point where the last person with direct experience of a historical event dies, leaving only second-hand knowledge of the event. Usually applied to wars as the veterans of each war pass away, but can be applied to any significant event that leaves a lasting imprint on a society. Once an event has passed its Memory Event Horizon it will forevermore only exist in history books and documentaries.

When the last U.S. veteran of World War I, Frank Buckles, passed away in 2011 the First World war passed the Memory Event Horizon into history.